A robot control device for controlling a robot is required to comply with various safety standards. A countermeasure against overvoltage failures of an input power source is one of the requirements.
Conventionally, as an overvoltage protection countermeasure applied to a power-supply circuit for complying with the safety standards, one of following methods is adopted:
(1) A power-supply product with a safety certification acquired from a third-party organization is used; and
(2) A power-supply product with no safety certification acquired from a third-party is adopted and an overvoltage protection function is added to the power-supply product later.
Out of the above methods, the method (1) is easy as a measure for achieving the overvoltage protection countermeasure. However, the method (1) has problems such as a purchase price is significantly higher than the power-supply product with no safety certification acquired from the third party.
Meanwhile, the method (2) can be achieved fairly less expensively as compared with the method (1). Therefore, generally, it is more likely to apply the method (2) to achieve compliance with the safety standard.
As a measure for achieving the overvoltage protection countermeasure, Patent Literature 1 listed below describes an overvoltage protection circuit in which, when an excessively large voltage is input by mistake, a surge absorber breaks in a short-circuit mode to surely cause melting of a fuse, for example.
Further, Patent Literature 2 listed below describes an overvoltage protection circuit in which, when an input voltage reaches a predetermined value or more, the input voltage exceeds a Zener voltage of a Zener diode and the Zener diode becomes electrically conductive, so that a thyristor is short-circuited and an overcurrent flows through a current fuse, causing the current fuse to be an open state (to melt).